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i was feeding my guineas like normal, you know the regular routine, I noticed something on Chocco’s ear, it doesn’t make sense he seemed totally fine. What could it be and what couldve caused it?
Should I seperate him from his cage mate?
and is it a fungus or infection?
That looks likely to be a fungal infection. A vet can do a proper assessment and prescribe a prescription cream to clear it up. Make sure to wash your hands really well, as some fungi (like ringworm) can be spread between guinea pigs and people. You'll also want to scrub the cage really well once treatment begins to ensure you kill any remaining spores. Separating is really up to you... that looks like a little pig and separating may be traumatic for him and his cagemate has already been exposed. I would probably be apt to keep them together but keep a close eye on both pigs for any flaky skin, hair loss, or other signs of fungal infection.
I agree with @Freela.
Please do not try to treat it at home and get him along to a vet as soon as possible.
If you try to treat it on spec it could make it harder to properly diagnose and take longer to clear up.
Although it is impossible to diagnose with just a picture, it does look like it could be fungal, so best to practice good hygiene when you handle your pigs and also take both of them along when you go to the vet.
Good luck, and don't forget to let us know ho you get on.